This invention relates to high speed automated testing of electronic devices such as integrated circuits. More particularly, it relates to a nestless linear transport that grips and plunges a device to be tested onto a test circuit board or socket while maintaining alignment of the device leads to the respective test connectors of the circuit.
In the manufacture of electronic components, such as integrated circuits (“IC's”), it is necessary to test the completed IC before shipment and/or before assembly into a product, e.g. a printed circuit board used in a computer or consumer electronics product. Production economics require that the test be reliable and performed with a high throughput rate.
Typically the devices are stored and tested in specialized containers such as elongated plastic tubes (“sticks”) arranged on trays, or held in sockets or other fixtures. For testing, the devices are fed to a test site where they are presented to a test fixture, such as a socket or contactor assembly, which in turn has a set of electrical contacts that make electrical connection between the device under test (“DUT”) and a test circuit. The device can be moved to the fixture, or the reverse. Common architectures for handling the DUT's include pick and place apparatus and gravity feed apparatus. A typical gravity feed test handler 12′ (shown in FIGS. 1A and 1B) unloads devices from a “stick” to a vertical test track 14′ where they fall, in succession, to a test site 16′ defined by a set of movable pins or equivalent stop members that selectively projects into and is then withdrawn from the track. A transport, here a plunge mechanism 10′, then grips the DUT at the test site 16′, carries it to the test circuit 18′, and drives its leads into engagement with the contacts of the test circuit. The test is performed, and then the device is returned to the test site position and released to one of several output tracks depending on the results of the test. The plunger is then positioned to grip and transport the next DUT in another cycle of operation.
The devices are often small. The leads can bend out of position or be misformed or mispositioned. Contaminants such as oxides can coat the leads and degrade the quality of the electrical connection. Many modem devices are “small outline (“SO”) chips where the electrical lead or pad is flush with the plastic or ceramic body of the device (“leadless”). To ensure a good electrical connection, usually a spring or other engagement force and/or a wiping engagement between the lead and the contact, are used. The drive force of the transport also promotes the quality of the electrical connection. A reliable, accurate alignment of the DUT with respect to the test circuit contacts is important not only to establish a good electrical connection at each connection, but also to control cross talk between adjacent pins.
For radio frequency (“RF”) devices, high-speed memory chips, and others, the physical location of the DUT with respect to its test circuit is important. With high-speed devices, for example, the test signals are extremely fast rising. That creates inductance problems in all but very short transmission lines. Close physical proximity of the DUT to the test circuit, thus simulating the actual end-use environment, decreases the test time and increases the reliability of the test. An on-going design problem in high-speed, automated testing of many modem devices is the trade-off between 1) the need to place the DUT into a test circuit with close proximity to other circuit elements and simulating as closely as possible the actual end-use operating environment, and 2) the need to move the DUT to this location while at the same time aligning its leads with associated connectors as the test circuit (e.g., a p.c. board) or a test socket or contactor assembly mounted on and connected to the test circuit board.
One known solution has been to grip a DUT, but to do so “lightly”, allowing movement of the DUT as it engages the test fixture or site. Fixed guide or cam surfaces then “steer” the DUT into the correct alignment for test connections. Projecting locator pins are also widely used to align, and then secure an alignment of, a DUT, or a socket or a tray holding a DUT in a known location and orientation. These pins and surfaces, however, take up space at the test site. In particular, they are near the DUT, and create a “keep out” area around the DUT that spaces test circuit components from the DUT when it is connected.
Vacuum suction gripping is also known, e.g., to pick and place a DUT or DUT's, as well as to hold a device, test fixture, or other components. U.S. Pat. No. 5,344,737 is a recent example of vacuum suction used to secure components in IC fabrication. U.S. Pat. No. 6,211,960 is another recent example where vacuum suction is used as an element of an apparatus that aligns and connects objects such as semiconductor components and substrates. In the '960 patent, a set of actuators guided by a vision control system, locate and orient an object on a moving platform with multiple degrees of freedom of motion.
In the context of a plunge-type presentation of the DUT, it is known to use a “nest”, that is, a frame of an insulating, usually elastomeric, static dissipative material that surrounds and is closely spaced from the DUT. In one form, a small rectangular frame of an elastomer is secured on the test board around the test site. A rigid frame piece overlies the elastomer and secures its location. The DUT is gripped and plunged through this frame and the nest, which guide the DUT into alignment, and reject any grossly misaligned DUT's that approach the test site. It is also known to mount a nest such as nest 22 (FIGS. 1A and 1B) on a plunge mechanism in order to frame the DUT in a desired position and to interact with a test site to guide and align the DUT. The nest typically includes holes that engage locator pins on the test circuit board or a test socket to establish and maintain the proper alignment between the DUT and connectors of the test circuit or socket. While such nested arrangements can perform well in certain applications, the DUT cannot be in close physical proximity to the circuit and adjacent components of the circuit as required for the testing of many devices such as the RF chips mentioned above.
It is therefore an object of the invention to provide a nestless plunge apparatus and method that transports IC's and the like to a test site and provides the requisite degree of reliability of alignment and electrical connection to the test circuit while also placing substantially no restrictions on the proximity of the device to the test circuit.
Another object is to provide the foregoing advantages with reliability.
A further object is to provide the foregoing advantages in a variety of handler environments.
Still another object is to provide the foregoing advantages as well as convenient adjustability to handle and test devices of different sizes and types, and is especially well suited to test small leadless IC device packages.